The present invention relates in general to a writing instrument of the kind comprising an ink reservoir and a nib holder pipe adapted to support a writing nib in the form of a needle or hair wire at one end of the reservoir and positioned to receive ink by capillary action from an ink carrier in the reservoir, and more particularly to an improved structure of the longitudinal writing nib axially slidably held in the nib holder pipe, with one end of the nib projecting from and resiliently retractable in the nib holder pipe.
A conventional writing instrument of the type described above is disclosed in U.S. Pat. No. 4,364,684, assigned to the present assignee, in which an ink permeable resilient seat member is inserted into a concave portion formed within a holder which holds slidably the writing nib. This structure is desirable in a sense that it provides a reliable axial movement due to the effect of the resilient seat member. On the other hand, the insertion of the resilient seat member as disclosed in the aforementioned U.S. Pat. No. 4,364,684 requires a higher degree of precision of the seat member, and provides some difficulties and increased labor.
An attempt has been made to provide a resilient writing nib so that the nib is axially and resiliently displaceable, as disclosed in unexamined Japanese Utility Model Application No. 54-85109, published Jan. 13, 1981 under Pub. No. 56-3684 and assigned to the present assignee. This structure does not necessitate, as separate members, the resilient seat member and a weight which forces movement of the nib by gravity, thus its entire structure can be simplified.
By the way, it is desirable that a movement force (or in other words a resilient force) of the writing nib be relatively small so as to minimize wearing of a tip of the writing nib. In order to lessen the movement force of the writing nib, an attempt has been made to minimize the diameter of the writing nib. However, it has been found that the writing nib of reduced-diameter induces much more wearing of the nib.